The present invention relates to a vehicle steering apparatus, and more particularly, to a steer-by-wire steering apparatus. The present invention also pertains to a method for controlling the apparatus.
A steer-by-wire steering apparatus is known as a steering apparatus for controlling steered wheels of vehicles. In a typical steer-by-wire steering apparatus, a steering wheel is mechanically separated from a steering gearbox coupled to steered wheels, or front wheels, of a vehicle. That is, the steering wheel is not directly coupled to the steering gearbox. The steering gearbox is driven by an electric motor in accordance with a detected angle of the steering wheel, or a steering wheel angle.
Such a steering apparatus is provided with a backup control system that allows steering to be reliably performed when the apparatus malfunctions. For example, there has been proposed a backup control system having two redundant control systems (see Japanese Laid-Open Patent Publication No. 2002-37112).
One of the control systems functions as a main control system, while the other control system functions as an auxiliary control system. The auxiliary control system has a similar configuration as the main control system. Each control system includes an electric motor for actuating a steering rod coupled to the steered wheels, a drive circuit for driving the motor, a control circuit for controlling the electric motor through the drive circuit, and sensors necessary for performing control.
When the control systems are functioning normally, the motors of the control systems are driven without interfering each other. The electric motors of the main and the auxiliary control systems actuate the steering rod in accordance with the steering wheel angle.
When the main control system malfunctions, the electric motor of the main control system is stopped. Then, the electric motor of the auxiliary control system actuates the steering rod.
When the one of the control systems malfunctions and the other control system takes over the control, a warning lamp is lit to inform the driver of the malfunction of one of the control systems. However, even if the warning lamp is lit, the steering apparatus gives to the driver the same steering feel as the case where both systems are functioning normally. Therefore, the driver can continue driving and steering with the warning lamp on. In this case, the steering rod is actuated by only one of the control systems. However, it is undesirable that the remaining system continues being used. Thus, it is necessary to cause the driver to realize speedily that there is a malfunction in the steering apparatus.